The present invention relates to an antireflection coating, and particularly relates to one which not only reduces the reflection of ambient light on the surface of a display screen of an indicator such as a vehicle meter or a display on a personal computer but also increases the contrast on the display screen, thereby enhancing the visibility of the information displayed on the display screen and reducing the stresses on the operator""s eyes.
FIGS. 4(a) and 4(b) are sectional views of two prior art antireflection coatings. Each is of an exemplary case where a single high refractive index layer 1 and a single low refractive index layer 2 are coated in superposition on a substrate 3.
The prior art antireflection coating 9 shown in FIG. 4(a) comprises the substrate 3 which is coated with the low refractive index layer 2 having a specified refractive index which in turn is coated with the high refractive index layer 1 having a higher refractive index than the low refractive index layer.
Incident light 5 (specifically, ambient light-falling on the surface of the display screen of an indicator), as it enters the high refractive index layer 1 and the low refractive index layer 2, is reflected first at the interface between air and the high refractive index layer 1 (this interface is hereunder referred to as the xe2x80x9cfirst interfacexe2x80x9d), then at the interface between the high refractive index layer 1 and the low refractive index layer 2 (this interface is hereunder referred to as the xe2x80x9csecond interfacexe2x80x9d), whereupon two beams of light reflection 4 are produced.
The optical thicknesses of the high refractive index layer 1 and the low refractive index layer 2 are so set that the reflected light 4 from the first interface has a phase difference of xc2xcxcex from the light 4 reflected from the second interface; hence, the two beams of light reflection 4 optically interface with each other to become attenuated.
By taking advantage of this optical interference effect, it has been possible to reduce the reflection of ambient light (i.e., external light) on the surface of the display screen of an indicator such as a vehicle meter or a display on a personal computer while enhancing the contrast on the display screen, thereby providing a display of better quality.
In the antireflection coating 9 shown in FIG. 4(b), a hard coating layer 6 having a comparable refractive index to the substrate 3 is provided between the substrate and the low refractive index layer 2 such as to cancel the fine asperities in the surface of the substrate 3, thereby providing it with a higher degree of smoothness.
The hard coating layer 6 adds to the aforementioned optical interference effect so that the reflection of ambient light (external light) on the surface of the display screen is further reduced while achieving a further increase in the contrast on the display screen so as to provide a display of better quality.
In each of the prior art antireflection coatings 9 described above, the light 4 reflected from the first interface and the light 4 reflected from the second interface optically interface with each other to become attenuated; however, the light 4 reflected from the interface between the low refractive index layer 2 and the substrate 3 (or between the low refractive index layer 2 and the hard coating layer 6, and this interface will be hereunder referred to as xe2x80x9cthird interfacexe2x80x9d) is not fully subjected to the above interference effect and the light 4 reflected from the third interface will be radiated in front of the substrate 3.
As a result, the reflected light 4 from the third interface causes a difficulty in that a reflected image due to the reflection of the ambient light appears on surface of the display screen of a vehicle meter or a display on a personal computer.
The reflected image causes the additional problem of reducing the contrast on the display screen and deteriorating the quality of the display produced.
The present invention has been accomplished in order to solve the aforementioned problems of the prior art, and an object of the invention is particularly to provide an antireflection coating on a substrate which is coated with a low refractive index layer having a specified refractive index which in turn is coated with a high refractive index layer having a higher refractive index than that low refractive index layer, which is either characterized in that a roughened surface which scatters and reflects the incident light entered into the low refractive index layer in contact with the substrate, is formed at the interface between the low refractive index layer and the substrate, or that a light-diffusing layer which scatters and reflects the incident light entered into the low refractive index layer in contact with the substrate, is formed at the interface between the low refractive index layer and the substrate, or that a hard coating layer in contact with the low refractive index layer is formed by dispersing a light-diffusing material in the hard coating layer, which scatters and reflects the incident light entered into the low refractive index layer. In either case, the reflected light from the third interface is scattered when it is radiated in front of the substrate, whereby the formation of a reflected image due to the reflection of the ambient light on the surface of the display screen of a vehicle meter or a display on a personal computer is effectively prevented to enhance the contrast on the display screen and produce a display of better quality.
According to a first aspect of the invention, an antireflection coating comprises one or more high refractive index layers having a specified refractive index which alternate with one or more low refractive index layers having a lower refractive index than that high refractive index layers, and is characterized in that a roughened surface which scatters and reflects the incident light entered into the terminal low refractive index layer, is formed on the surface of the terminal low refractive index layer.
According to a second aspect of the invention, an antireflection coating comprises a substrate which is coated with a low refractive index layer having a specified refractive index which in turn is coated with a high refractive index layer having a higher refractive index than that low refractive index layer, and is characterized in that a roughened surface which scatters and reflects the incident light entered into the low refractive index layer in contact with that substrate, is formed at the interface between that low refractive index layer and that substrate.
According to a third aspect of the invention, an antireflection coating comprises a substrate having a hard coating layer formed thereon, which layer is coated with a low refractive index layer having a specified refractive index which in turn is coated with a high refractive index layer having a higher refractive index than that low refractive index layer, and is characterized in that a roughened surface which scatters and reflects the incident light entered into the low refractive index layer in contact with that hard coating layer, is formed at the interface between that low refractive index layer and that hard coating layer.
According to the first to third aspects of the invention, the reflected light from the third interface is scattered by means of the roughened surface so that the formation of a reflected image due to the reflection of the ambient light (i.e., the reflected light) on the surface of the display screen of a vehicle meter or a display on a personal computer can be effectively prevented to enhance the contrast on the display screen and provide a display of better quality.
According to a fourth aspect of the invention, in the antireflection coating of the third aspect, that hard coating layer has a refractive index not higher than that of that substrate.
According to the fourth aspect of the invention, in addition to the advantages of the first to third aspects of the invention, the reflected light from the third interface is scattered more efficiently by means of the hard coating layer so that the formation of a reflected image due to the reflection of the ambient light (i.e., the aforementioned reflected light) on the surface of the display screen of a vehicle meter or a display on a personal computer can be prevented more efficiently to further enhance the contrast on the display screen and provide a display of even better quality.
According to a fifth aspect of the invention, an antireflection coating comprises one or more high refractive index layers having a specified refractive index which alternate with one or more low refractive index layers having a lower refractive index than that high refractive index layers, and is characterized in that a light-diffusing layer which scatters and reflects the incident light entered into the terminal low refractive index layer is formed on the surface of that low refractive index layer.
According to a sixth aspect of the invention, an antireflection coating comprises a substrate which is coated with a low refractive index layer having a specified refractive index which in turn is coated with a high refractive index layer having a higher refractive index than that low refractive index layer, and is characterized in that a light-diffusing layer which scatters and reflects the incident light entered into the low refractive index layer in contact with that substrate, is formed at the interface between that low refractive index layer and that substrate.
According to a seventh aspect of the invention, an antireflection coating comprises a substrate having a hard coating layer formed thereon, which layer is further coated with a low refractive index layer having a specified refractive index which in turn is coated with a high refractive index layer having a higher refractive index than that low refractive index layer, and is characterized in that a light-diffusing layer which scatters and reflects the incident light entered into the low refractive index layer in contact with that hard coating layer is provided at the interface between that low refractive index layer and that hard coating layer.
According to the fifth to seventh aspects of the invention, the reflected light from the third interface is scattered by means of the light-diffusing layer so that the formation of a reflected image due to the reflection of the ambient light (i.e., the aforementioned reflected light) on the surface of the display screen of a vehicle meter or a display on a personal computer can be effectively prevented to enhance the contrast on the display screen and provide a display of better quality.
According to an eighth aspect of the invention, in the antireflection coating of the seventh aspect, that hard coating layer has the same refractive index as that substrate.
According to the eighth aspect of the invention, in addition to the advantages of the fifth to seventh aspects of the invention, the reflected light from the third interface is scattered more efficiently by means of the hard coating layer so that the formation of a reflected image due to the reflection of the ambient light (i.e., the aforementioned reflected light) on the surface of the display screen of a vehicle meter or a display on a personal computer can be prevented more efficiently to further enhance the contrast on the display screen and provide a display of even better quality.
According to a ninth aspect of the invention, an antireflection coating comprises a substrate having a hard coating layer formed thereon, which layer is further coated with a low refractive index layer having a specified refractive index which in turn is coated with a high refractive index layer having a higher refractive index than that low refractive index layer, and is characterized in that the hard coating layer is formed with a light-diffusing material dispersed therein so as to scatter and reflect the incident light entered into the low refractive index layer in contact with that hard coating layer.
According to the ninth aspect of the invention, the reflected light from the third interface is scattered by means of the hard coating layer having a light-diffusing material dispersed therein so that the formation of a reflected image due to the reflection of the ambient light (i.e., the reflected light) on the surface of the display screen of a vehicle meter or a display on a personal computer can be effectively prevented to enhance the contrast on the display screen and provide a display of better quality.
According to a tenth aspect of the invention, in the antireflection coating of the ninth aspect, that coating layer has a refractive index not higher than that of that substrate.
According to the tenth aspect of the invention, in addition to the advantages of the ninth aspect of the invention, the reflected light from the third interface is scattered more efficiently by means of the hard coating layer having a light-diffusing material dispersed therein so that the formation of a reflected image due to the reflection of the ambient light (i.e., the aforementioned reflected light) on the surface of the display screen of a vehicle meter or a display on a personal computer can be prevented more efficiently to further enhance the contrast on the display screen and provide a display of even better quality.